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Conventional Organic Solvents (conventional + organic_solvent)
Selected AbstractsColloidal Noble-Metal and Bimetallic Alloy Nanocrystals: A General Synthetic Method and Their Catalytic Hydrogenation PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Shuyan Song Dr. Abstract A general single-step strategy has been developed for the direct thermal decomposition of noble-metal salts in octadecylamine to synthesize octahedron- and rod-shaped noble-metal aggregates and monodisperse noble-metal or bimetallic alloy nanocrystals without introducing any additive into the system. It has presented a facile and economic way to fabricate these nanocrystals, especially alloy nanocrystals, which does not require a post-synthesis solid-state annealing process. The morphology of the nanocrystals can be easily controlled by tuning the synthetic temperature. Their ability to catalyze heterogeneous Suzuki coupling reactions has been investigated and showed satisfactory catalytic activity. The catalytic performance of the monometallic and bimetallic alloy nanocrystals were also evaluated in the selective hydrogenation of citral in a conventional organic solvent (toluene) and a green solvent (supercritical carbon dioxide, scCO2). Interestingly, the catalysts performed differently to each other when they were in scCO2 owing to the different morphology, which should be readily optimized for further use. [source] Kinetic resolution of ibuprofen catalyzed by Candida rugosa lipase in ionic liquidsCHIRALITY, Issue 1 2005Yu Hongwei Abstract Candida rugosa lipase-catalyzed esterification of ibuprofen with 1-propanol was conducted in seven ionic liquids and the results were compared with those in isooctane. Although the enzyme showed comparable or higher activity in some ionic liquids compared to that in isooctane, only in the case of [BMIM]PF6 was the enantioselectivity (E = 24.1) almost twice that (E = 13.0) of isooctane. In another six ionic liquids the enzyme enantioselectivity was much poorer (E = 1.1,6.4). At the same conversion of 30%, E of [BMIM]PF6 is more than triple that of isooctane. The lipase stability in [BMIM]PF6 was improved by 25% of that in isooctane. It was concluded that [BMIM]PF6 could be applied to substitute the conventional organic solvent (isooctane) in the esterification of ibuprofen. Chirality 17:16,21, 2005. © 2004 Wiley-Liss, Inc. [source] Methods for stabilizing and activating enzymes in ionic liquids,a reviewJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2010Hua Zhao Abstract Ionic liquids (ILs) have evolved as a new type of non-aqueous solvents for biocatalysis, mainly due to their unique and tunable physical properties. A number of recent review papers have described a variety of enzymatic reactions conducted in IL solutions; on the other hand, it is important to systematically analyze methods that have been developed for stabilizing and activating enzymes in ILs. This review discusses the biocatalysis in ILs from two unique aspects (1) factors that impact the enzyme's activity and stability, (2) methods that have been adopted or developed to activate and/or stabilize enzymes in ionic media. Factors that may influence the catalytic performance of enzymes include IL polarity, hydrogen-bond basicity/anion nucleophilicity, IL network, ion kosmotropicity, viscosity, hydrophobicity, the enzyme dissolution, and surfactant effect. To improve the enzyme's activity and stability in ILs, major methods being explored include the enzyme immobilization (on solid support, sol,gel, or CLEA), physical or covalent attachment to PEG, rinsing with n -propanol methods (PREP and EPRP), water-in-IL microemulsions, IL coating, and the design of enzyme-compatible ionic solvents. It is exciting to notice that new ILs are being synthesized to be more compatible with enzymes. To utilize the full potential of ILs, it is necessary to further improve these methods for better enzyme compatibility. This is what has been accomplished in the field of biocatalysis in conventional organic solvents. Copyright © 2010 Society of Chemical Industry [source] Enhancement of activity and selectivity in lipase-catalyzed transesterification in ionic liquids by the use of additivesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2007Francisco J Hernández-Fernández Abstract BACKGROUND: Seven ionic liquids (ILs) based on 1-alkyl-3-methylimidazolium cation in combination with hexafluorophosphate and bis{(trifluoromethyl)sulfonyl}imide anions were tested as reaction media for lipase-catalyzed transesterification in low water conditions. With the aim of improving the activity and/or selectivity of the lipase, various treatments were applied to ionic liquid media such as equilibration with aqueous solutions of salts, NaHCO3 or Na2CO3, or the addition of a catalytic amount of a non-reactive organic base to the reaction mixture, triethylamine. RESULTS: The treated ionic liquids were shown to be excellent media for lipase-catalyzed ester synthesis by transesterification compared with conventional organic solvents, such as n -hexane. All treatments were found to enhance the synthetic activity of the enzyme, the best results being achieved with the addition of triethylamine. The addition of a catalytic amount of this base to the ILs resulted in a significant increase in both the synthetic activity and selectivity values. For instance, the synthetic activity in [emim+][TfN2,] was enhanced more than 12 times and the selectivity increased from 86% to 95% when triethylamine was used. CONCLUSION: These treatments could be easy-to-use approaches to improve the efficiency of enzymatic reactions in ionic liquids when the reaction does not proceed smoothly. Copyright © 2007 Society of Chemical Industry [source] Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensorsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Jichang Feng Abstract A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5,-Divinyl-2,2,-bipyridyl with tris(4-bromophenyl)amine and with 4,4,-dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, 1H NMR, and 13C NMR. The polymer HTP had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV,vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer-based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222,230, 2009 [source] Dissolution and Doping of Polyaniline Emeraldine Base in Imidazolium Ionic Liquids Investigated by Spectroscopic TechniquesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2007Fabio Rodrigues Abstract Polyaniline is a model molecular system in the study of conductive polymers. Ionic liquids, on the other hand, are becoming more and more a very convenient alternative for conventional organic solvents. The dissolution of polyaniline-emeraldine base (PANI-EB) in imidazolium ILs leads to its doping, as indicated by optical and resonance Raman spectroscopies. In this study, it is proposed that the interaction of PANI-EB and imidazolium ILs involves the specific interaction of the quinoid moiety of the former with the imidazolium ring of the latter, an interpretation that is also based on N K -edge XANES measurements of neat PANI-EB, neat ILs, and of their solutions. [source] Identification and quantitation of phenolic compounds in faecal matrix by capillary gas chromatography and nano-electrospray mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2006Ulrike Knust Very few relevant methods have been described for the detection and quantitation of phenolic compounds in faecal matrix. Extraction with conventional organic solvents such as chloroform/methanol (2:1, Folch reagent), methanol and ethanol (72%) showed high extraction efficiency for lipids and also gave good recovery of the major phenolic compounds present in the matrix. However, in comparison with a newly developed phosphate buffer method, the yield of minor phenolics was negligible when detected by these conventional methods. Conventional methods also lead to contamination of the ion source of the mass spectrometer and rapid deterioration of column performance mostly due to the high concentration of lipids. However, if the faecal matrix is initially extracted with phosphate buffer, and the extract acidified and re-extracted with diethyl ether, the range and yield of phenolic compounds are enhanced and the problem of lipid contamination is substantially alleviated. Following pilot studies and optimisation of the procedure, individual phenolic compounds (n,=,29) were identified by nano-electrospray ionisation mass spectrometry (nano-ESI-MS), nano-ESI-tandem mass spectrometry (MS/MS) and gas chromatography/mass spectrometry (GC/EI-MS) and quantitated (n,=,27) by GC/MS in subsets (n,=,5) of faecal samples, collected during the European Agency for Cancer Prevention calcium/fibre intervention study from four European countries (Italy, Germany, Spain and Denmark). A range of phenolic compounds (mainly acids) was detected, dominated by phenylacetic, benzoic, phenylpropionic and m -hydroxyphenylpropionic acids, representing on average 9.91 (93%), 8.25 (92%), 9.45 (95%) and 11.05 (98%) mM in the Italian, German, Spanish and Danish samples, respectively. The new method should enable large epidemiologic, case-control and intervention studies on the relevance of phenolic antioxidants in the aetiology of colorectal cancer to be conducted in the future. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||